Emission standards for unburned hydrocarbons, carbon monoxide and nitrogen oxide contaminants continue to become more stringent. In order to meet such standards, catalytic converters containing a three-way conversion (TWC) catalyst are located in the exhaust gas line of internal combustion engines. Such catalysts promote the oxidation by oxygen in the exhaust gas stream of unburned hydrocarbons (HC) and carbon monoxide (CO) as well as the reduction of nitrogen oxides (NOx) to nitrogen. Generally, TWC catalysts substantially simultaneously oxidize carbon monoxide and hydrocarbons and reduce nitrogen oxide.
Many TWC catalysts are manufactured with at least two separate catalyst coating compositions (washcoats) that are applied in the form of aqueous dispersions as successive layers on a substrate (for example, a honeycomb body composed of ceramic or metal) in order to separate platinum group metals (PGM) such as palladium and rhodium, which represent the main catalytically active species. Separation has been considered necessary because palladium and rhodium can form an alloy, which is known to be less catalytically active.
U.S. Patent Appln. Pub. No. 2014/0205523, incorporated herein by reference, is directed to automotive catalyst composites having a two-metal containing layer, where the two-metal containing layer is formed from a single washcoat layer. This washcoat layer contains two PGMs, each of which is on its own support, resulting in a homogeneous mixture of the two supported PGMs in the same layer. This layer is coated on a carrier.
There is a continuing need to provide TWC catalysts composites that utilize metals (e.g., PGMs) efficiently and remain effective to meet regulated HC, NOx, and CO conversions.